Concentrating solar power with glasshouses

ABSTRACT

A protective transparent enclosure (such as a glasshouse or a greenhouse) encloses a concentrated solar power system (e.g. a thermal and/or a photovoltaic system). The concentrated solar power system includes one or more solar concentrators and one or more solar receivers. Thermal power is provided to an industrial process, electrical power is provided to an electrical distribution grid, or both. In some embodiments, the solar concentrators are dish-shaped mirrors that are mechanically coupled to a joint that enables rotation at a fixed distance about respective solar collectors that are fixed in position with respect to the protective transparent enclosure. In some embodiments, the solar collectors are suspended from structure of the protective transparent enclosure and the solar concentrators are suspended from the solar collectors. In some embodiments, the greenhouse is a Dutch Venlo style greenhouse.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.13/146,910, filed on Mar. 10, 2012, entitled “CONCENTRATING SOLAR POWERWITH GLASSHOUSES” which is a 371 U.S. national phase ofPCT/US2010/022780 filed on Feb. 1, 2010, entitled “CONCENTRATING SOLARPOWER WITH GLASSHOUSES” which claims benefit of priority to U.S.Provisional Application No. 61/149,292 filed Feb. 2, 2009, entitled“CONCENTRATING SOLAR POWER WITH GLASSHOUSES” and U.S. ProvisionalApplication No. 61/176,041, filed May 6, 2009, entitled “CONCENTRATINGPHOTO VOLTAICS WITH GLASSHOUSES”, each of which are herein incorporatedby reference in their entirety.

BACKGROUND

Field

Advancements in concentrated solar thermal power (CST), photovoltaicsolar energy (PV), concentrated photovoltaic solar energy (CPV), andindustrial use of concentrated solar thermal energy are needed toprovide improvements in performance, efficiency, and utility of use.

Related Art

Unless expressly identified as being publicly or well known, mentionherein of techniques and concepts, including for context, definitions,or comparison purposes, should not be construed as an admission thatsuch techniques and concepts are previously publicly known or otherwisepart of the prior art. AU references cited herein (if any), includingpatents, patent applications, and publications, are hereby incorporatedby reference in their entireties, whether specifically incorporated ornot, for all purposes.

Concentrated solar power systems use mirrors, known as concentrators, togather solar energy over a large space and aim and focus the energy atreceivers that convert incoming solar energy to another form, such asheat or electricity. There are several advantages, in some usagescenarios, to concentrated systems over simpler systems that directlyuse incident solar energy One advantage is that more concentrated solarenergy is more efficiently transformed to heat or electricity than lessconcentrated solar energy. Thermal and photovoltaic solar receiversoperate more efficiently at higher incident solar energy levels Anotheradvantage is that non-concentrated solar energy receivers are, in someusage scenarios, more expensive than mirror systems used to concentratesunlight. Thus, by building a system with mirrors, total cost ofgathering sunlight over a given area and converting the gatheredsunlight to useful energy is reduced.

Concentrated solar energy collection systems, in some contexts, aredivided into four types based on whether the solar energy isconcentrated into a line-focus receiver or a point-focus receiver andwhether the concentrators are single monolithic reflectors or multiplereflectors arranged as a Fresnel reflector to approximate a monolithicreflector.

A line-focus receiver is a receiver with a target that is a relativelylong straight line, like a pipe. A line-focus concentrator is areflector that receives sunlight over a two dimensional space andconcentrates the sunlight into a significantly smaller focal point inone dimension (width) while reflecting the sunlight withoutconcentration in the other dimension (length) thus creating a focalline. A line-focus concentrator with a line-focus receiver at its focalline is a basic trough system. The concentrator is optionally rotated inone dimension around its focal line to track daily movement of the sunto improve total energy capture and conversion.

A point-focus receiver is a receiver target that is essentially a point,but in various approaches is a panel, window, spot, ball, or othertarget shape, generally more equal in width and length than a line-focusreceiver. A point-focus concentrator is a reflector (made up of a singlesmooth reflective surface, multiple fixed facets, or multiple movableFresnel facets) that receives sunlight over a two-dimensional space andconcentrates the sunlight into a significantly smaller focal point intwo dimensions (width and length). A monolithic point-focus concentratorwith a point-focus receiver at its focal point is a basic dishconcentrated solar system. The monolithic concentrator is optionallyrotated in two dimensions to rotate its focal axis around its focalpoint to track daily and seasonal movement of the sun to improve totalenergy capture and conversion.

A parabolic trough system is a line concentrating system using amonolithic reflector shaped like a large half pipe. The reflector has a1-dimensional curvature to focus sunlight onto a line-focus receiver orapproximates such curvature through multiple facets fixed relative toeach other.

A concentrating Fresnel reflector is a line concentrating system similarto the parabolic trough replacing the trough with a series of mirrors,each the length of a receiver, that are flat or alternatively slightlycurved in their width. Each mirror is individually rotated about itslong axis to aim incident sunlight onto the line-focus receiver.

A parabolic dish system is a point concentrating system using amonolithic reflector shaped like a bowl. The reflector has a2-dimensional curvature to focus sunlight onto a point-focus receiver orapproximates such curvature through multiple flat or alternativelycurved facets fixed relative to each other.

A solar power tower is a point concentrating system similar to theparabolic dish, replacing the dish with a 2-dimensional array of mirrorsthat are flat or alternatively curved. Each mirror (heliostat) isindividually rotated in two dimensions to aim incident sunlight onto apoint-focus receiver. The individual mirrors and an associated controlsystem comprise a point-focus concentrator whose focal axis rotatesaround its focal point.

In solar thermal systems, the receiver is a light to heat transducer.The receiver absorbs solar energy, transforming it to heat andtransmitting the heat to a thermal transport medium such as water,steam, oil, or molten salt. The receiver converts solar energy to heatand minimizes and/or reduces heat loss due to thermal radiation. Inconcentrated photovoltaic systems, the receiver is a photovoltaicsurface that directly generates electricity from sunlight. In some solarthermal systems, CPV and CST are combined in a single system where athermal energy system generates thermal energy and acts as a heat sinkfor photovoltaic cells that operate more efficiently when cooled. Otherreceivers, such as a Stirling engine, that use solar energy to generateheat and then locally convert the heat to electricity through mechanicalmotion and an electric generator, are also deployed as a receiver, insome approaches.

In some concentrated solar systems, such as some systems with highconcentration ratios, overall system is cost dominated by variouselements such as the concentration system (such as a mirror or lens), asupport system for the concentrators, and motors and mechanisms thatenable tracking movement of the sun. The elements dominate the costsbecause the elements are enabled to withstand wind and weather. In someusage scenarios, solar energy systems are enabled to withstand variousenvironmental dangers such as wind, rain, snow, ice, hail, dew, rodents,birds and other animals, dust, sand, moss, and other living organisms.Reflectivity of a concentrator is sensitive to damage, tarnishing, anddirt buildup since only directly reflected sunlight, not scatteredsunlight, is effectively focused.

Glass mirrors are used in some concentrated systems, because of anability to maintain good optical properties over long design lives (e.g.30 years) of concentrated solar systems. Glass is relatively fragile andvulnerable to hail and other forms of damage unless it is suitablythick, e.g. 4-5 mm for relatively larger mirrors. In a 400 square footconcentrating dish the thickness results in a weight of close to 1000lbs or about nine kg per meter of concentrator area. The mirror isformed in a precise curve, in one dimension for a trough, in twodimensions for a dish, to focus sunlight.

In some concentrated systems, mirror surfaces cease to focus as intendedif warped. Thus, the reflector is supported and held in shape by a metalsuperstructure that is shaped to the curved glass. The superstructuresupports and protects the mirror from environmental conditions such aswinds of 75 mph or more. The winds add an additional 10,000 lbs of loadbeyond the 1000 lb weight of the mirror, resulting in complexconstruction requiring roughly 20 kg of structural steel for every meterof mirror area in a dish system.

In some concentrated systems, concentrator tracking motors move the 30kg per square meter weight of the concentrator, and also overcome forceof wind that exceeds an additional 300 kg per sq meter. The motors areexposed to environmental elements (such as, dirt, dust, moisture, etc).

In some CST systems, parabolic dishes with point-focus receivers are notused, at least in part because structural demands on the dish areprohibitive and designing a tracking mechanism that keeps the focalpoint fixed (to avoid complex and expensive mechanisms to connect thethermal medium system) is impractical.

SUMMARY

The invention may be implemented in numerous ways, including as aprocess, an article of manufacture, an apparatus, a system, and acomposition of matter. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. The Detailed Description provides an exposition of one ormore embodiments of the invention that enable improvements inperformance, efficiency, and utility of use in the field identifiedabove. The Detailed Description includes an Introduction to facilitatethe more rapid understanding of the remainder of the DetailedDescription. As is discussed in more detail in the Conclusions, theinvention encompasses all possible modifications and variations withinthe scope of the issued claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an overview of an embodiment of a greenhouse-enclosedconcentrated solar thermal system providing heat to a factory housing anindustrial process.

FIG. 2 illustrates a perspective cutaway view of selected details of anembodiment of an enclosing greenhouse and an enclosed concentrated solarenergy system.

FIG. 3 illustrates a perspective cutaway view of selected details of anembodiment of an enclosing greenhouse with point-focus solarconcentrators inside arranged in a rhombic lattice pattern.

FIGS. 4A and 4B illustrate selected details of an embodiment of agreenhouse enclosure with enclosed solar concentrators and solarreceivers in respective incident sunlight contexts, high angle (summer)and low angle (winter).

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures illustrating selecteddetails of the invention. The invention is described in connection withthe embodiments. The embodiments herein are understood to be merelyexemplary, the invention is expressly not limited to or by any or all ofthe embodiments herein, and the invention encompasses numerousalternatives, modifications, and equivalents. To avoid monotony in theexposition, a variety of word labels (including but not limited to:first, last, certain, various, further, other, particular, select, some,and notable) may be applied to separate sets of embodiments; as usedherein such labels are expressly not meant to convey quality, or anyform of preference or prejudice, but merely to conveniently distinguishamong the separate sets. The order of some operations of disclosedprocesses is alterable within the scope of the invention. Wherevermultiple embodiments serve to describe variations in process, method,and/or features, other embodiments are contemplated that in accordancewith a predetermined or a dynamically determined criterion performstatic and/or dynamic selection of one of a plurality of modes ofoperation corresponding respectively to a plurality of the multipleembodiments. Numerous specific details are set forth in the followingdescription to provide a thorough understanding of the invention. Thedetails are provided for the purpose of example and the invention may bepracticed according to the claims without some or all of the details.For the purpose of clarity, technical material that is known in thetechnical fields related to the invention has not been described indetail so that the invention is not unnecessarily obscured.

A. Introduction

This introduction is included only to facilitate the more rapidunderstanding of the Detailed Description; the invention is not limitedto the concepts presented in the introduction (including explicitexamples, if any), as the paragraphs of any introduction are necessarilyan abridged view of the entire subject and are not meant to be anexhaustive or restrictive description. For example, the introductionthat follows provides overview information limited by space andorganization to only certain embodiments. There are many otherembodiments, including those to which claims will ultimately be drawn,discussed throughout the balance of the specification.

In some circumstances, techniques described herein enable cost reductionof concentrated solar power systems. In various embodiments, collection(concentration and conversion of solar energy) is separated fromprotection. A protective transparent exoskeleton (such as a glasshouseor a greenhouse) surrounds and/or encloses collecting elements (oralternatively the collecting elements are placed in the exoskeleton),enabling the collecting elements (mirrors, lenses, etc) to be lessrobust than otherwise required. By separating collecting and protectingfunctions, and leveraging off-the-shelf technology (e.g. highlyengineered, cost effective, and proven greenhouse technology, such asglass growers greenhouse technology) for the protection function, insome circumstances a reduction in cost and complexity of a system (suchas mirrors/lenses, support structure, foundations, tracking mechanisms,etc.) is enabled with a relatively minimal impact on overallperformance. The glasshouse is relatively low to the ground with littlewind force bearing surfaces, and is designed to withstand wind andweather with a relatively minimal structural skeleton. Because theglasshouse reduces wind forces acting on the collector and receiverelements, the mirrors or lenses used for collection and concentrationinside the exoskeletal protection of the glasshouse are enabled to belightweight, in some embodiments to a point of seeming flimsy, and thusare relatively less costly to construct, transport, support and aim, andhave little or no weatherization costs. Note that within thisdisclosure, the terms glasshouse and greenhouse are usedinterchangeably, and are not meant to necessarily imply any sort ofhorticultural activity.

Protected embodiment techniques described herein are applicable tovarious concentrated solar power systems (e.g. a line-focus receiverwith a single monolithic reflector, a line-focus receiver with multiplereflectors arranged as a Fresnel reflector, a point-focus receiver witha single monolithic reflector, or a point-focus receiver with multiplereflectors arranged as a Fresnel reflector, and more generally any ofthe approaches described in the background section) on an industrialscale. The protected embodiment techniques enable reflectors built fromlighter materials with simpler and lighter frames since wind, weather,and UV light are reduced inside a glasshouse enclosure. Foundation,suspension, and tracking mechanisms for receivers and concentrators areenabled to be simpler, lighter, and less expensive.

Some embodiments of a concentrated solar system inside a glasshouse havean array of relatively large 3-D-freedomed, 2-D-solar-tracking parabolicdishes suspended from fixed roof locations, reminiscent of invertedinside-mirrored umbrellas focusing tracked sunlight onto receivers atthe “handles” that are fixed relative to each umbrella bowl. Someembodiments have an array of 0-D-solar-tracking (fixed position)concentrators. Some embodiments have an array of 1-D-solar-tracking,fixed line—focusing, parabolic troughs. Some embodiments have an arrayof fixed target point-focus power towers each with an associated arrayof suspended or floor mounted reflectors that together with anassociated control system, embody a point-focus solar concentrator.

A glasshouse, such as a commercial greenhouse, efficiently supports flatglass planes. Supporting framework of straight metal sections brace eachother and attach to the ground in multiple places. Some glasshousesdesigned to withstand the same weather conditions as an externalparabolic dish require less than half as much structural steel (lessthan 10 kg) per square meter of concentrator, compared to an externalparabolic dish. Total weight, including 4-5 mm glass, is less than 20 kgper square meter of concentrator, for the glasshouse.

According to various embodiments, concentrators are made entirely orpartially of thin-gauge aluminum foil, reflective film, or otherrelatively reflective and lightweight materials. Some of the materialshave higher reflectivity than glass mirrors. Concentrators, in someembodiments, are foam core combined with reflective material, enablingconcentrators weighing less than one kg per square meter. Lightweightconstruction, in some usage scenarios, reduces one or more of costsassociated with production, transportation, and installation ofconcentrators. Total weight for some enclosed concentrated solar energyembodiments (including exoskeleton and protected collector) is less than20 kg per square meter of concentrator.

The glasshouse structure is primarily fixed and immobile, and trackingsystems control and aim the less than one kg per square meterconcentrators inside the structure in an environment having relativelysmall wind forces.

In some embodiments, a commercial greenhouse is a suitable enclosure astaught by the techniques described herein. Growers have determined thatfor many types of plants, 1% less light reaching plants equals 1% lesscrop growth and hence profit. Greenhouse designs are optimized to reducecost, structural shading, glass reflective losses, and glasstransmission losses. In some usage scenarios, the structural shading,glass reflective losses, and glass transmission losses cause a majorityof lost sunlight. The Dutch Venlo design is relatively efficient atreducing the losses. Options available in commercial greenhouses includelow-shading structural design, anti-reflective glass coatings (to reducereflective losses), and low-iron glass (to reduce transmissive losses).

In some embodiments, sunlight losses due to a glasshouse enclosure areless than 20% at 33 degrees latitude without an anti-reflective coatedglass. In some embodiments using anti-reflective coated glass, lossesare 13%. In some embodiments, techniques described herein improvesalvage value of a system in one or more of obsolescence, abandonment,and destruction and/or damage due to storm, ice, corrosion, andearthquake events.

A commercial greenhouse has multiple uses and has, in some embodimentsand/or usage scenarios, a ready sale market for a greenhouse sold inplace or for relocation. In some embodiments, a greenhouse enclosure ofa concentrated solar energy system is a significant portion of thesystem cost. Resale value of the greenhouse, in some usage scenarios,lowers overall risk of a solar energy project and/or reduces financingcosts.

In some embodiments, point concentrating systems are advantaged overother systems by providing high concentration ratios for a given levelof focusing effort due to focusing in two dimensions. In someembodiments, fixed receivers are advantaged over other systems to avoidcomplex and expensive mechanisms such as moving fluid joints or hoses toconnect the thermal medium system. In some embodiments and/or usagescenarios, selected components (such as receivers or pipes) that arefixed during a tracking mode of operation are permitted to move or aremoved due to expansion and contraction of materials or for cleaningduring a maintenance mode of operation. In some embodiments, parabolicdish systems are advantaged over heliostats due to simplicity of movingand aiming a monolithic concentrator.

Thermal conduction and convection increase with wind speed, thusreducing efficiency of solar thermal receivers. In some non-enclosedconcentrated system approaches, solar energy receivers are protectedfrom environmental effects including heat loss and physical damage by anat least partially transparent protective enclosure for each receiver.In some enclosed embodiments, thermal energy receivers are enabled tominimize heat loss without using an enclosure for each receiver.

B. Concentrated Solar Energy System Usage Scenario

FIG. 1 illustrates an overview of an embodiment of a greenhouse-enclosedconcentrated solar thermal system providing heat to a factory housing anindustrial process. A concentrated solar energy system is enclosedwithin greenhouse 101 and providing thermal energy to industrial process125 (such as housed in a factory). A concentrated solar energy system isconnected through inlet pipe 108 and outlet pipe 109 to optional storagesystem 124. The outlet pipe carries a thermal medium that has beenheated by the concentrated solar energy system to the storage system andthence on to industrial process 125. The inlet pipe carries coolerthermal medium back to the concentrated solar energy system for heating.In embodiments lacking an optional storage system, the outlet and inletpipes are connected directly to the industrial process. Any portions ofthe pipes, both inside and outside the enclosure, are optionallythermally insulated to reduce heat loss.

Various industrial processes consume significant amounts of heat attemperatures generated by some embodiments of a concentrated solarenergy system described herein. The industrial processes includeelectricity generation, seawater desalination, and drywallmanufacturing. Storage system 124 is optionally included in the systemand includes a reservoir for heated thermal medium and optionallyincludes a reservoir for cooler thermal medium waiting to return to theconcentrated solar energy system for heating. Storing pre-heated thermalmedium in the storage unit enables continuation of industrial processesbetween sunset and sunrise, and through overcast weather. Stick figureperson 113 illustrates a scale of the system (with respect to greenhouseheight as well as concentrator size and spacing) in some embodiments.

C. Concentrated Solar Energy System

Industrial scale concentrated solar power systems, in some embodiments,cover multiple acres of land, with large-scale systems practical in thehundreds of acres. FIG. 2 illustrates a perspective cutaway view ofselected details of an embodiment of an enclosing greenhouse and anenclosed concentrated solar energy system. Illustrated greenhouse 201has low internal shading and low cost. According to various embodiments,the greenhouses are less than an acre to hundreds of acres in size.Suitable commercial greenhouses are available with short lead times fromvarious vendors. Additionally, in some usage scenarios, there is amarket for used greenhouses, enabling relatively easier financing oflarge-scale concentrated solar energy projects, such as describedherein. Elements of the greenhouse include a roof system with multiplepeaks and gutters (such as peak 202 and gutter 203). The roof system isenabled to drain water efficiently from the roof structure, to keepincident angles of sunlight relatively close to directly normal totransparent roof material to reduce reflection, and to keep roof supportmembers in compression. Sidewalls of the greenhouse (such as sidewall204) further enclose interior space of the greenhouse and havetransparent covering where sunlight is incident thereon and areoptionally of any appropriate material where little sunlight isincident. The greenhouse structure is enabled to keep most wind, rain,and other environmental elements from the interior, and is optionallynot entirely weather tight. Optional fan driven overpressure filtrationsystem 205 optionally provides relatively clean pressurized air to theinterior to further inhibit infiltration of dust and other elements tothe interior. The lack (or reduction) of dust reduces or eliminates aneed to clean concentrators (such as concentrator 210), reducingoperating costs and enabling use of less robust and less scratchresistant reflective concentrator materials, in some usage scenariosand/or embodiments.

In some embodiments, all elements of the concentrated solar energysystem are located within a protected interior of a greenhouse.Greenhouse transparent cover material 220 is glass or any materialgenerally transparent to sunlight. The transparent cover optionallyincludes an ultra violet (UV) blocking coating or film to enable use ofplastics inside the greenhouse (such as reflective plastic mirror filmsfor the concentrator surfaces) that would otherwise break downrelatively rapidly. Solar receivers (such as solar receiver 206) arearranged in a lattice pattern throughout the interior space. In someembodiments, solar receivers are held at somewhat fixed positions duringsunlight collecting operation to reduce a need for flexible jointscarrying a thermal medium. The solar receivers are interconnectedthrough a series of thermally insulated pipes (such as pipe 207). Thepipes carry thermal medium from inlet 208, where colder thermal mediumflows into the system, to outlet 209, where heated thermal medium flowsout. In a concentrated solar thermal (CST) system, heated thermal mediumis a primary output of the system and is fed to an industrial process.In a direct electric system, such as a concentrated photo voltaic (CPV)system, a thermal medium optionally provides cooling to PV cells orother aspects of the receiver. Excess heat in the thermal medium of aCPV system is optionally used in an industrial process. Measurement andcontrol wires, power for motors, and various cabling is routed with thethermal medium pipes, in some CST and CPV embodiments.

Solar receivers are enabled to focus sunlight according to variousfocusing techniques, such as line focus or point focus. In FIG. 2,point-focus solar receivers are illustrated arranged in an array and aresuspended from pipes 207 that are in turn suspended from the roof of theenclosing greenhouse. Point-focus solar concentrators are suspended fromassociated solar receivers (e.g. solar concentrator 210 is suspendedfrom solar receiver 206) so that the focal point of the concentrator isheld relatively fixed on the receiver while the concentrator bodyremains free to rotate around the receiver in two degrees of freedom totrack daily and seasonal motions of the sun. The arrangement ofrelatively fixed receivers and concentrators that rotate around thereceivers to track the sun is enabled, at least in part, by low weightof the concentrators and absence of wind forces on the concentrators.

D. Rhombic Lattice Pattern

FIG. 3 illustrates a perspective cutaway view of selected details of anembodiment of enclosing greenhouse 301 with point-focus solarconcentrators inside arranged in a rhombic lattice pattern. Solarreceivers (such as solar receiver 306) and point-focus solarconcentrators (such as point-focus solar concentrators 310) are arrangedin a rhombic lattice pattern to cover relatively efficiently the groundwith a tessellated lattice of concentrators. Horizontal pipes (such ashorizontal pipe 307) are arranged along greenhouse floor 311 with localfeeder pipes connecting to and suspending each receiver (such as localfeeder pipe 312 suspending solar receiver 306). Stick figure person 313illustrates a scale (with respect to greenhouse height as well asconcentrator size and spacing) in some embodiments.

E. Incident Sunlight Transmission

In some embodiments, solar concentrators as large as will fit insidelarge standard commercial greenhouses, roughly in the six meter aperturerange, are used. Each solar concentrator is associated with a drivemechanism and a solar receiver, thus increasing concentrator size(correspondingly reducing how many are used in a particular area)reduces the number of the drive mechanisms and/or the solar receivers,reducing cost overall. In various embodiments, one or more concentratorsshare a same drive mechanism.

Irradiance characterizes power of incident electromagnetic radiation(such as sunlight) at a surface, per unit area. Some sunlight lossescaused by the greenhouse enclosure glass and structural shading aredetermined by comparing direct normal sunlight received inside thegreenhouse enclosure (interior) with unimpeded direct normal sunlightreceived outside the greenhouse enclosure (exterior). In absolute terms,irradiance loss is highest at midday; considered relatively, theirradiance loss is highest in mornings and evenings. FIGS. 4A and 4Billustrate selected details of an embodiment of a greenhouse enclosurewith enclosed solar concentrators and solar receivers in respectiveincident sunlight contexts, high angle (summer) and low angle (winter).FIG. 4 A illustrates a side view of a greenhouse in a context ofincident sunlight 414A at a relatively high angle in the sky (e.g.during summer). The greenhouse is situated so that roof peaks (such asroof peak 402) and roof gutters (such as roof gutter 403) run mostlyeast to west and wall 415 roughly faces the equator. Thus, incidentsunlight mainly strikes both equator facing roof faces (such as equatorfacing roof face 416) and pole facing roof faces (such as pole facingroof face 417) at an angle relatively close to a respective normal axisof each (equator facing and pole facing) roof face around noon. Lightstriking glass at an angle greater than approximately 70 degrees off thenormal axis of the glass is largely reflected, reducing an amount ofsolar energy a system is enabled to capture. Solar receivers aresuspended from roof peaks (such as solar receiver 406 suspended fromroof peak 402) but offset (in some embodiments) slightly toward theequator to more efficiently accommodate seasonal aiming of solarconcentrators (such as solar concentrator 410). The solar concentratorsare held at a seasonally adjusted height so that at least a portion ofincident sunlight 414A is reflected (such as reflected sunlight 418A)and is then concentrated on the solar receivers.

FIG. 4B illustrates the system of FIG. 4A in a context of incidentsunlight 414B at a relatively low angle in the sky (e.g. during winter).The solar concentrators are positioned with their upper edges (such asupper edge 419) positioned close to the pole facing roof faces of thegreenhouse, so the concentrator are aimed at incident sunlight 414B toreflect at least a portion of the incident sunlight (such as reflectedsunlight 418B) onto the solar receivers.

During the winter, almost all of the incident sunlight 414B strikes theequator facing roof faces. The angle of the incident sunlight inrelation to the equator facing roof face is less than 70 degrees aroundnoon, enabling relatively high energy transmission. A synchronoustracking movement of the solar concentrators (such as in a tracking modeduring daylight hours) enables capturing a relatively high fraction ofthe incident sunlight. In some embodiments, solar concentrators areenabled to sometimes partly shade one another significantly in thewinter months (as illustrated) because the concentrators are relativelyinexpensive. The shading enables relatively close concentrator spacing,and provides a relatively high clustering or light exploitation factor,enabling relatively efficient energy recovery throughout the year.

F. Selected Greenhouse Details

In some embodiments, the greenhouse includes roof peaks (such as roofpeak 402) that in combination with included roof gutters (such as roofgutter 403A) are enabled to drain water over a large space and to angletransparent roof material relatively close to direct normal to incidentsunlight in summer and in winter. A roof system with peaks and guttersis referred to as a “ridge and furrow” style roof, in some usagescenarios, and in some embodiments is a form of a “gutter-connected”roof system. The greenhouse includes support columns (such as supportcolumn 421A). Some of the support columns are arranged around theperiphery of the greenhouse and others of the support columns arearranged within the greenhouse. In some embodiments, the greenhouseincludes support columns at every roof gutter (such as support columns421A, 421, and 421B located at roof gutters 403A, 403, and 403B,respectively, of FIG. 4A). In alternate embodiments, every other supportcolumn is omitted (such as support columns 421 A and 421B being omitted)and trusses (such as truss 422) are horizontal lattice girders. Roofgutters without support columns are floating gutters (e.g. roof gutters403A and 403B). Some of the embodiments that omit every other supportcolumn are implemented with a Venlo style greenhouse. Variousembodiments suspend pipes and receivers from trusses or horizontallattice girders. Various embodiments suspend pipes from trusses orhorizontal lattice girders and further suspend receivers from pipes.

G. Selected Embodiment Details

In various embodiments and/or usage scenarios, the illustratedembodiments are related to each other. For example, in some embodiments,greenhouse 101 of FIG. 1 is an implementation of greenhouse 201 of FIG.2, with inlet pipe 108 and outlet pipe 109 corresponding respectively toinlet 208 and outlet 209. For another example, in some embodiments,various elements of FIGS. 4A/4B are implementations of elements in otherfigures, such as roof peak 402, roof gutter 403, solar receiver 406,thermally insulated pipes 407, and solar concentrator 410, correspondingrespectively to peak 202, gutter 203, receiver 206, thermally insulatedpipe 207, and solar concentrator 210 of FIG. 2.

While the forgoing embodiments are described as having roof systems withpeaks and gutters, other embodiments use alternate roof systems, such aspeaked, arched, mansard, and Quonset-style roof systems, as well asvariations and combinations thereof. In various embodiments, a partiallytransparent protective enclosure (such as a glasshouse or a greenhouse)uses glass to provide the transparency, and other embodiments usealternative transparent materials such as plastic, polyethylene,fiberglass-reinforced plastic, acrylic, polycarbonate, or any othermaterial having suitable transparency to sunlight and sufficientstrength (in combination with a supporting framework) to provideenvironmental protection.

H. Conclusion

Certain choices have been made in the description merely for conveniencein preparing the text and drawings and unless there is an indication tothe contrary the choices should not be construed per se as conveyingadditional information regarding structure or operation of theembodiments described. Examples of the choices include: the particularorganization or assignment of the designations used for the figurenumbering and the particular organization or assignment of the elementidentifiers (the callouts or numerical designators, e.g.) used toidentify and reference the features and elements of the embodiments.

The words “includes” or “including” are specifically intended to beconstrued as abstractions describing logical sets of open-ended scopeand are not meant to convey physical containment unless explicitlyfollowed by the word “within.”

Although the foregoing embodiments have been described in some detailfor purposes of clarity of description and understanding, the inventionis not limited to the details provided. There are many embodiments ofthe invention. The disclosed embodiments are exemplary and notrestrictive.

It will be understood that many variations in construction, arrangement,and use are possible consistent with the description, and are within thescope of the claims of the issued patent. The names given to elementsare merely exemplary, and should not be construed as limiting theconcepts described. Also, unless specifically stated to the contrary,value ranges specified, maximum and minimum values used, or otherparticular specifications, are merely those of the describedembodiments, are expected to track improvements and changes inimplementation technology, and should not be construed as limitations.

Functionally equivalent techniques known in the art are employableinstead of those described to implement various components, sub-systems,operations, functions, or portions thereof.

The embodiments have been described with detail and environmentalcontext well beyond that required for a minimal implementation of manyaspects of the embodiments described. Those of ordinary skill in the artwill recognize that some embodiments omit disclosed components orfeatures without altering the basic cooperation among the remainingelements. It is thus understood that much of the details disclosed arenot required to implement various aspects of the embodiments described.To the extent that the remaining elements are distinguishable from theprior art, components and features that are omitted are not limiting onthe concepts described herein.

All such variations in design are insubstantial changes over theteachings conveyed by the described embodiments. It is also understoodthat the embodiments described herein have broad applicability to otherapplications, and are not limited to the particular application orindustry of the described embodiments. The invention is thus to beconstrued as including all possible modifications and variationsencompassed within the scope of the claims of the issued patent.

We claim:
 1. A solar collection system, comprising: an enclosure havinga transmissive surface positioned between an exterior region of theenclosure and an interior region of the enclosure to transmit solarradiation from the exterior region to the interior region, wherein theenclosure is not air tight; a solar receiver positioned in the interiorregion within the enclosure; and a pressure source coupled in fluidcommunication with the interior region to pressurize the interior regionabove a pressure in the exterior region.
 2. The system of claim 1wherein the transmissive surface includes at least one of glass,plastic, polyethylene, fiberglass-reinforced plastic, acrylic, andpolycarbonate.
 3. The system of claim 1 wherein the pressure source iscoupled in fluid communication with the interior region to at leastrestrict entry of materials from the exterior region into the interiorregion.
 4. The system of claim 1 wherein the pressure source is coupledin fluid communication with the interior region to provide relativelyclean pressurized air to the interior region to inhibit infiltration ofdust and other elements into the interior region.
 5. The system of claim1, further comprising a filter in fluid communication with the pressuresource to remove particulates from air directed into the enclosure. 6.The system of claim 1 wherein the pressure source includes a fan.
 7. Thesystem of claim 1 wherein the receiver includes a line-focus receiver.8. The system of claim 1, further comprising a reflector positioned toreceive solar radiation passing into the enclosure through thetransmissive surface, and direct at least a portion of the radiation tothe receiver.
 9. The system of claim 8 wherein the reflector includes aparabolic reflector.
 10. The system of claim 8 wherein the reflector issuspended from an overhead structure of the enclosure.
 11. The system ofclaim 8 wherein the reflector includes curved glass.
 12. The system ofclaim 8 wherein the reflector has a non-glass reflective surface. 13.The system of claim 1 wherein the receiver carries a working fluid thatincludes water.
 14. A method for collecting solar energy, comprising:receiving radiation at a solar receiver positioned within an interiorregion of a non-airtight enclosure, after the radiation has passedthrough a transmissive surface of the enclosure; directing a thermaltransport medium through the solar receiver to heat the thermaltransport medium; and pressurizing an interior region of the enclosureabove a pressure of an exterior region outside the enclosure.
 15. Themethod of claim 14 wherein the transmissive surface includes at leastone of glass, plastic, polyethylene, fiberglass-reinforced plastic,acrylic, and polycarbonate.
 16. The method of claim 14 whereinpressurizing the interior region includes at least restricting entry ofmaterial from the exterior region into the interior region.
 17. Themethod of claim 14 wherein pressurizing the interior region includesproviding relatively clean pressurized air to the interior region toinhibit infiltration of dust and other elements into the interiorregion.
 18. The method of claim 14 wherein the material includes dust.19. The method of claim 14 wherein pressurizing includes pressurizingwith a fan.
 20. The method of claim 14 wherein the thermal transportmedium includes water.
 21. The method of claim 14, further comprisingfiltering air entering the interior region.
 22. The method of claim 14,further comprising reflecting the radiation toward the receiver afterthe radiation has passed through the transmissive surface.
 23. Themethod of claim 22 wherein reflecting includes reflecting with aparabolic surface.
 24. A method for making a solar collection system,comprising: building a non-airtight enclosure having a transmissivesurface positioned between an exterior region of the enclosure and aninterior region of the enclosure to transmit solar radiation from theexterior region to the interior region; positioning a solar receiver inthe interior region within the enclosure; and coupling a pressure sourcein fluid communication with the interior region to pressurize theinterior region above a pressure in the exterior region.
 25. The methodof claim 24 wherein the transmissive surface includes at least one ofglass, plastic, polyethylene, fiberglass-reinforced plastic, acrylic,and polycarbonate.
 26. The method of claim 24 wherein coupling thepressure source includes coupling the pressure source in fluidcommunication with the interior region to at least restrict entry ofmaterials from the exterior region into the interior region.
 27. Thesystem of claim 24 wherein coupling the pressure source includescoupling the pressure source in fluid communication with the interiorregion to provide relatively clean pressurized air to the interiorregion to inhibit infiltration of dust and other elements into theinterior region.
 28. The method of claim 24 wherein the pressure sourceincludes a fan.
 29. The method of claim 24, further comprising couplinga filter in fluid communication with the pressure source and theinterior region to filter air directed into the interior region by thepressure source.
 30. The method of claim 24, further comprisingpositioning a reflector to reflect radiation passing through thetransmissive surface toward the receiver.